Radar on the high seas

Modern maritime radar systems for missile defense and navigation have become more precise by leveraging commercial signal processing and radio frequency (RF) components in modular designs that enable commonality with clear technology refresh paths.

Superior radar capability is key to enabling an effective missile defense, as adversarial threats continue to grow in complexity and capability. In the maritime domain this dominance is even more crucial as the U.S. and its allies look to upgrade their maritime missile-defense and radar capability to counter the aggressiveness of North Korea and China.

Demands are also being placed on designers of maritime navigation radar to improve the accuracy and performance of their systems, especially in high-clutter environments.

In both cases, radar system designs are leveraging commercial components and building modular systems.

Maritime missile defense

Modularity and open architectures are important to the design of the Enterprise Air Surveillance Radar (EASR) from Raytheon, which is being outfitted on all Gerald R. Ford-class aircraft carriers and amphibious warships by the U.S. Navy. EASR enables simultaneous anti-air and anti-surface warfare, electronic protection, and air-traffic-control capabilities, Raytheon says.

The system takes advantage of the highly scalable design and mature technologies of Raytheon’s AN/SPY-6(V) Air and Missile Defense Radar (AMDR). Taking advantage of modularity, both EASR and AMDR have been built with the same individual building blocks, which Raytheon dubs Radar Modular Assemblies (RMAs).

“Each RMS is roughly 2 feet by 2 feet by 2 feet in size, and is a standalone radar that can be grouped to build any size radar aperture – from a single RMA to configurations larger than currently fielded radars,” says Scott Spence, director of Naval Radar Systems for Raytheon.

The AMDR consists of 37 RMAs, equivalent to SPY-1D(V) +15 dB in terms of sensitivity, according to Raytheon, which essentially means that the SPY-6 can see a target of half the size at twice the distance of today’s radars. Meanwhile, the EASR is a 9-RMA configuration – which is equivalent to the sensitivity of the current SPY-1D(V) radar on today’s destroyers, and at only 20 percent of the size of the older SPS-48.

Array size, or the number of RMAs needed, can be customized to the mission needs of a ship to provide it with the capability “to spot and defeat potential threats such as ballistic missiles, cruise missiles, airborne adversaries, surface threats, electronic threats, or any com­bina­tion of them,” Spence notes. “Its cooling, power, command logic, and software are all scalable, which allows for new instantiations without significant radar development costs.”

Using a wideband digital beamforming radar “supports better target detection and discrimination,” he adds. “Adaptive, wideband digital beamforming and radar-signal/data-processing functionality provides exceptional capability in adverse conditions, such as high clutter and jamming environments. It’s also reprogrammable to adapt to new missions or emerging threats.”

Two variants of EASR are being designed with each facing an identical 9-RMA array: Variant 1 will be a single-face, rotating radar replacing AN/SPS-48 and -49 air search radars. It will be the primary sensor for ship self-defense and situational awareness and the designated radar for the LHA-8 and LX(R) platforms. Variant 2 will be three-face, fixed-array radar replacing AN/SPY-4 Volume Search Radar. It will be the primary sensor for ship self-defense, situational awareness, and air-traffic control. It will also be the designated radar for Gerald R. Ford-class supercarriers, starting with CVN 79.

Commonality between the radar systems and open architectures plays an important role in the design of the EASR.

The SPY-6(V) features a fully programmable, back-end radar controller unit built out of commercial off-the-shelf (COTS) x86 processors. “This programmability allows the system to adapt to emerging threats,” Spence says. “And the commercial nature of the x86 processors simplifies obsolescence replacement – as opposed to costly technical refreshes/upgrades and associated downtime – which are savings that lower radar sustainment costs during each ship’s service life. The radar’s open architecture also facilitates integration with existing and future combat-management systems.” Designed for maintainability, standard line-replaceable unit (LRU) replacement in the RMA can be accomplished in under six minutes – requiring only two tools.

Leveraging commercial semiconductor technology such as gallium nitride (GaN) has also enabled the advanced performance capabilities of the EASR, as well the AMDR.

Beyond GaN, Raytheon engineers also leveraged distributed receiver exciters and adaptive digital beamforming in the EASR design. GaN components cost 34 percent less than gallium arsenide (GaAs) alternatives, deliver higher power density and efficiency, and have shown mean time between failures at 100 million hours, according to Raytheon says.

Navigation and merchant marine radar

“Lower-end systems are becoming less modular in hardware and more modular in software,” says Tim Acland, chief engineer for Kelvin Hughes, a U.K.-based company that specializes in the design and manufacture of navigation and surveillance systems. “Modularity in older systems was to enable repair of assemblies most likely to fail. The market de­mand now is for products that don’t re­quire maintenance. Modularity also allows flexible product configurability, which is more often achieved in software these days than in hardware. Scalability is less common than in the past, although where it’s required the trend is toward open interfaces and COTS hardware for expansion. And where larger systems are required, retaining highly integrated custom hardware for lower-scale systems.”

High-performance navigation and surveillance sensors “are increasingly being needed to perform more challenging roles – such as ice detection, oil-spill detection, diver/swimmer detection, drone detection and tracking, and target classi­fication,” Acland says. “These roles require even more signal processing than their primary role and, in some cases, require more data to be extracted from target returns.” (Figure 1.)

Figure 1: X-Band SharpEye radar transceivers from Kelvin Hughes enable clutter suppression through use of a patented pulse sequence, pulse compression, and radar-return processing to ensure that the radar operator is presented with targets and tracks on the display, while minimizing the clutter from the severest of rainstorms and high sea states.

“The digitization boundary continues to move closer to the point of the radar RF carrier frequency,” Acland adds. “This exploits the trends in higher-sampling-frequency analog-to-digital converters (ADCs) at a price point that is within reach of the unit build cost of the systems.” Digitization at higher frequencies and wider bandwidths shifts the focus “away from traditional analogue signal processing and more toward digital signal processing,” Acland says. “As Moore’s Law marches on, transistor density and price point continue to enable more digital signal processors per IC at a given price point.”

“Lower-cost, high-volume radars are being developed from hardware and software stacks provided as development kits and supported heavily by field-application engineers and internal developers of the large silicon IC manufacturers,” Acland says. “The software stacks include IP blocks such as FFTs [fast Fourier transforms], FIR [finite impulse response] filters, operating systems, and even prepackaged board support for low- to mid-level software frameworks. The software development toolsets for developing on these platforms are increasingly integrated by the supplier of the target software.”

Midlevel sensors use a similar design approach, according to Acland, but with less involvement from silicon manufacturers. “The design life cycles are longer, integration levels lower, and the emphasis is on product flexibility,” he says.

“High-end sensors are using COTS DSP PCBs [printed circuit boards] – reducing the integration of the manufacture in favor of concentrating on developing novel high-performance processing routines – to implement and optimize low-level DSP in-house, ahead of the generic IP block available on the market,” Acland explains. “This effort is focused in software rather than in developing DSP-processing PCBs.

“Development life cycles of products are also typically much longer at the high end versus low-end, which makes COTS a solution that supports products through a long service and sales lifetime – without significant changes to software. In this type of market, COTS hardware life cycles may be down to a few years, while core software functions may last more than 20 years.”